Pressure Effect on the Optical Spectra of Some One-Dimensional Pt-Complexes

The absorption and luminescence spectra of the polycrystalline magnesium, barium, and potassium salts of tetracyano platinate (II) were measured at hydrostatic pressures up to 5.4 kbar. These three salts showed an anomalously large red shift with pressure in both the absorption and luminescence spectra. The X-ray powder diffraction measurement was carried out for the magnesium salt up to 70 kbar. At 70 kbar the Pt–Pt distance decreased from 3.16 Å to 2.93 Å, 7.3% in linear compressibility. In the low pressure region up to ∼20 kbar, the Pt–Pt distance was observed to decrease greatly. The intramolecular transition 5dz2→6pz energy was calculated as a function of the Pt–Pt distance. By comparing the calculated and observed values, such a large red shift in the absorption spectra was tentatively explained in terms of electrostatic stabilization of the intramolecular transition 5dz2→6pz due to the decrease of the intermolecular distance and due to the consequent increase of the 5dz2→6pz intermolecular CT character.